基于直接调制DPSSL和MIMO-OFDM的水下无线光通信系统研究

如何高效地产生高速、大功率的绿光信号是水下无线光通信（UWOC）的技术难点。二极管泵浦固体激光器（DPSSL）具有高功率、高光束质量、工作稳定等优点，但调制带宽低，其直接调制能力长期被忽视。本项目提出直接调制DPSSL（DM-DPSSL）这一新概念，并通过正交频分复用（OFDM）、多输入多输出（MIMO）等技术提高系统传输速率与鲁棒性。从速率方程和基本电磁理论出发，针对制约DPSSL调制带宽的因素及基于MIMO-OFDM技术的应对策略进行深入的理论与实验研究，揭示DM-DPSSL工作机理以及与MIMO-OFDM技术有机结合的一般规律。探索水体参数变化对光信号传输的影响机理，提出动态环境下典型海水信道的理论模型及对基于DM-DPSSL和MIMO-OFDM的UWOC系统进行仿真分析和系统设计的一般方法。实验验证所设计的UWOC系统在干净海水中可传输100 m以上，速率达1 Gb/s以上。

The elegant generation of high-speed and high-power green-light signals is a technical challenge in the field of underwater wireless optical communication (UWOC). Diode-pumped solid-state lasers (DPSSLs) feature high power, good beam quality and strong robustness. However, the feasibility of directly modulating a DPSSL has long been ignored, due to its narrow modulation bandwidth. In this project, we propose a novel concept of directly modulated DPSSL (DM-DPSSL). In order to improve the bit rate and robustness of the UWOC system, orthogonal frequency-division multiplexing (OFDM) and multiple-input multiple-output (MIMO) technologies are adopted. Starting from laser rate equations and basic electromagnetic theories, we will conduct a comprehensive study on the major limiting factors of the DPSSL’s modulation bandwidth as well as the possible solutions based on MIMO-OFDM technologies. The study will reveal the underlying working principles of a DM-DPSSL and the general rules of applying MIMO-OFDM on a DM-DPSSL. We will further study the impact of different parameters of water on the high-speed optical signal generated by the DM-DPSSL, and build theoretical models of a variety of typical UWOC channels. We will achieve a general rule on the simulation and design of a UWOC system based on DM-DPSSLs and MIMO-OFDM. We will experimentally demonstrate that the designed UWOC system can realize a 100-m or above transmission in clean sea water at a bit rate of 1 Gb/s or above.